As one of the automatic tool changing devices U.S. Pat. No. 3,218,706 can be at first exemplarily indicated, wherein a proposition is made to dispose a tool changing arm between the tool magazine mounted on the frame and the spindle. The tool changing arm in this example pulls out a tool which has been used in the immediately previous operation from the spindle to return the same into the tool magazine before selecting another tool suitable for the next operation from the tool magazine to fix the same to the spindle.
In this kind of tool changing devices the tool changing arm is obliged to follow several complicated steps for one round of tool changing, normally requiring a fairly long time.
Another example of a tool changing device can be seen in U.S. Pat. No. 3,600,777 wherein a plurality of tools are attached, equally spaced from each other, to the tool magazine rotatably supported on the spindle head, and the tool magazine is situated such that one of the plurality of tools comes on the axial line of the spindle to be selected for attachment to the spindle by means of an axial movement of the spindle.
Since in this device many tools are closely arranged side by side, one operation with the selected tool is liable to invite a damage of a tool by a collision or touching of the work (to be machined) with any one of the other tools not selected.
As a practicable way of avoiding this kind of trouble, enlarging of the spacing between the neighboring tools can be taken with a sacrifice of reducing the number of tools arranged in the tool magazine. A device for enabling the spindle to move in the axial direction for connecting the spindle with the selected tool is apt to become complex in its interior structure.